Starboard side Exhaust Manifold warmer than Port side, 2000 4.3 Mercruiser

Hi All,
I was out last weekend and noticed that one exhaust manifold (starboard side) is warmer than the port side (never really checked this before so not sure if this is normal or not). My engine temp gauge was running about 174 - 173 deg F all day even while pulling tow-able tubes. Starboard side is warm while running, port side is cool while running. I pulled my exhaust manifolds (one piece style) off last night and checked them out, i have an inspection camera with 1/4" camera and cable so i was able to get into the manifold pretty good, nothing seemed to be plugged up or cracked. I also ran water through from the bottom hose fitting, it ran through and out no problem. I also replace the water shutters both sides of the Y-pipe recently (one was missing half of the flapper) I also used the camera then to inspect the Y-pipe and exhaust bellows for the missing half, nothing found.
Any words of wisdom?

Thanks.

The cool side is getting more water than the hot side, so it's either plugged someplace (restricting flow) or it's not getting enough water from the pump.

Ran into this just recently. A missing vane from a bad impeller was restricting the flow at the thermostat housing. I found that out by pulling the hoses off and idling the motor--more water came out one side..

Jeff

gjackman said:

Any words of wisdom?

Click to expand...

First, take Jeff's advice.
It may be as simple as finding the loose or broken previous impeller vanes, and installing a new seawater pump impeller.


It's tempting to restrict the coolant flow at the side that is running cooler.
I'd suggest that you DO NOT do this.
Instead, try to find a way to open up or "Un-Restrict" the side that is running warmer.





.

First off it is not unusual for one side to run 20 degrees "warmer" than the other.......Nature of the system

If one is cool to the touch and the other is very much hotter (like 50 degrees) and it almost burns your hand in a few seconds than you have an issue.

Thanks for the advice, I will try to do some checking this weekend. Maybe use an infrared temp gun to check the temp difference.

Now, that's a really good idea! I never leave the slip without mine.

Jeff

I tend to agree with Jack.

However, even though it is acceptible to see a slight difference in temps between one side and the other...... this does not mean that it cannot be corrected.

As I suggested earlier, DO NOT restrict the cooler side... instead, find a way to open up or UN-Restrict the warmer side.

Sometimes the T-stat housing is the culprit.... sometimes it's interior delamination at a one of the hoses...... sometimes it may be a fitting...... or the seawater transfer ports being plugged up (rust scale) more so at one side than the other.

Also, (and I think that this was mentioned) if an impeller blade had come loose at one time, and made it's way down stream into the system, it may have lodged itself in a passage.
These are fun to find!


.

That's why I tell people to change impellers!

Jeff

Ok, I put the exhaust manifold back on and test ran the engine with ear muffs on the driveway, ran it up to temp. About 173 deg F, checked the temp of both exh. Manifolds, starboard was about 130 F and pirt about 95 F. I lso noticed that the water coming from the thermostat housing to each exhaust manifold was a different temp 115-120 F on starboard and 85-90 F on port. Is that normal or could this indicate a thermostat or housing problem. I did replace my impeller two seasons ago, only put on about 20 hours last season and so far about 15 hours this year.

..."the water coming from the thermostat housing to each exhaust manifold was a different temp 115-120 F on starboard and 85-90 F on port."

That is NOT normal! Why...search me, but that's the problem. There's gotta to be a restriction inside the T-stat housing or something.

Jeff

post a picture of your thermostat housing showing the hoses and connection so we can tell what design you have.

Then we can suggest possible answers.

Here is my thermostat housing with the hose connections.

You have a fixed orifice system, meaning the output to the two hoses that feed each manifold (one each side) have a fixed hole size for water to pass thru.

Remove the hoses that feed the manifolds and check hole size on each side. Make sure they are the same.

If they are,

remove thermostat housing and check for blockage to either side and see if there is a diverter (piece of plastic) and if so see if it may be out of position meaning it is partially blocking one sides water flow........

If all is good the manifolds would be suspect...........

Not much else there...........

Look here for a parts structure of the thermostat housing...........it is for a 5.0 but is still the same as yours......it shows the plastic piece I refer to.

Item # 6

http://www.marineengine.com/parts/m...99/standard-cooling-system-fuel-cooled-system

Thanks for the help, I will try and inspect this in a couple of days. Will keep you posted.
Even if my manifolds are OK, it looks like it might be in my best interest to replace them with the two piece style with the risers. I may look at doing this in the off season since we are running out of warm days up here, only another 4 weeks left.

Thanks again.